This invention relates to an air intake system for a two cycle engine and more particularly to an improved scavenging system for a two cycle engine and particularly one having multiple cylinders.
The advantages of two cycle engines due to their simplicity is, of course, well known. However, the porting arrangement of such two cycle engines makes it essential that good exhaust scavenging be accomplished so as to achieve good running of the engine and good fuel efficiency. In connection with achieving good scavenging, it frequently is the practice to have some of the intake charge also pass out of the exhaust port. Obviously, this does not provide optimum performance.
An arrangement has been proposed wherein the intake charge is introduced into the chamber in such a way so as to minimize the amount of intake charge which is discharged through the exhaust port while at the same time insuring that the exhaust charge is fully scavenged. Such a system introduces the charge directly into the cylinder through the cylinder liner without passing through the crankcase. However, the systems of this type previously proposed have employed complicated valve arrangements for controlling the flow which adds to the cost of the engine and further somewhat limits the other practical arrangement for achieving this result and the overall engine construction. Also, the previously proposed does not permit either crankcase precompression or supercharging.
It is, therefore, a principal object of this invention to provide an improved scavenging arrangement for a two cycle internal combustion engine wherein complete scavenging is insured and wherein it will be insured that none of the fresh intake charge passes out of the exhaust port.
It is a further object of this invention to provide an improved induction system for a two cycle engine that will improve scavenging.
In conjunction with the use of scavenging of the type described so as to achieve good scavenging and minimum loss of fresh intake charge, the use of multiple scavenge ports is advantageous. The positioning and servicing of such multiple scavenge ports is difficult with constructions of the type previously employed. Also, the use of multiple scavenging passages has been limited to arrangements embodying crankcase compression.
It is, therefore, a further object of this invention to provide an arrangement for permitting the use of multiple scavenge passages without requiring crankcase compression.
It is a further object of this invention to provide a scavenge manifolding system for a two cycle engine that permits the servicing of multiple scavenge ports.
One way in which multiple scavenge ports can be employed is by providing a scavenging manifold that at least in part extends around the circumference of the cylinder bore. The individual scavenge passages are then served by this scavenge manifold. Although this arrangement has a high degree of utility, its application to multiple cylinder engines can give rise to some problems. Specifically, if this concept is utilized with multiple cylinder engines, then the engine length can be unduly increased. Alternatively, if the scavenge passages for adjacent cylinders have common portions, then there is a danger that the individual scavenge ports may not be served equally by the manifold.
It is, therefore, a still further object of this invention to provide an improved induction system for a two cycle engine having multiple cylinders.
It is a further object of this invention to provide an improved and compact induction system for multiple cylinder two cycle internal combustion engines.
The output of a two cycle engine can be increased by forcing the intake charge into the engine by some form of compressing device such as a supercharger or turbo charger. However, when such forced induction is employed, the scavenging problems become more acute. That is, when a high pressure intake charge is inducted into the combustion chamber, there is a greater risk that a substantial portion of the compressed air charge will pass out of the exhaust ports.
It is, therefore, a further object of this invention to provide an improved induction system and scavenging arrangement for a forced induction two cycle engine.
It is a further object of this invention to provide a forced induction system for a two cycle engine and porting arrangement therefor that will insure that the fresh air charge is not exhausted during the time when the exhaust and intake ports are open while yet insuring good scavenging.
In order to further improve the fuel efficiency of a two cycle engine, the use of fuel injection has been proposed. Although direct cylinder injection is common, the use of direct cylinder injection may not always insure equal distribution of the fuel in the combustion chamber. Also, the fuel discharge from the injector should be in such a way that fuel will not be discharged through the exhaust port during such times as the exhaust port is open. Therefore, there are certain advantages to indirect fuel injection such as the injection of fuel into the induction system rather than into the combustion chamber. However, when this is done, it also should be done in such a way as to insure against the discharge of fuel through the exhaust ports during the scavenging operation.
It is, therefore, a still further object of this invention to provide an improved arrangement for injecting fuel into a two cycle engine that will not cause fuel to be discharged from the exhaust ports during the scavenging operation.